Zoom lens assembly

ABSTRACT

A zoom lens assembly for projecting images from an object plane to the image plane at magnifications from approximately 17 times to approximately 29 times and operating in the wavelength range from 0.38 to 0.54 microns. The zoom lens assembly comprises four members, including a front fixed member, two cam controlled moving members, and a rear fixed member. A diaphragm is mounted within the rear moving member and is controlled by a third cam to maintain a constant f/number aperture at the long conjugate. In a preferred embodiment, the cams which control the movable members are designed so that equal angular rotations of the cam sleeve into which the cam slots are cut changes the magnification by equal amounts.

Bennett et al.

t/ [4 1 Aug. 26, 1975 ZOOM LENS ASSEMBLY v Primary ExaminerRonald L.Wibert [75] Inventors: Harold F. Bennett, Pasadena; AssistantExamineromad Clark w Li, Arlen! both f C lif Attorney, Agent, orFzrm-James J. Ralabate; Terry J.

, Anderson; Irving Keschner [73] Assignee: Xerox Corporation, Stamford,

Conn- 57 ABSTRACT [22] Filed: Oct. 23, 1973 A zoom lens assembly forprojecting images from an object plane to the image plane atmagnifications from [211 Appl' 408777 approximately 17 times toapproximately 29 times and operating in the wavelength range from 0.38to 0.54 [52 US. Cl. 350/184 microns. The zoom lens assembly com risesfour 1 P [51] Int. Cl. G02B /00 members, including a front fixed member,two cam [58] Field of Search 350/184, 186 controlled moving members, anda rear fixed member. A diaphragm is mounted within the rear movin memg56 References Cited ber and is controlled by a third cam to maintain acon- 1 UNITED STATES PATENTS stant f/number aperture at the longconjugate. in a 3 558 225 1/1971 Kuchhofi. 350H84 preferred embodiment,the cams which control the 3609005 9/1971 350H84 movable members aredesigned so that equal angular rotations of the cam sleeve into whichthe cam slots are cut changes the magnification by equal amounts.

5 Claims, 7 Drawing Figures I4 I ,2 RI #2 K m2 R14 R/ R22 R7 R23 8 l0fill Ma n/ [6 ma 32/ I i Fl; T

3 r f I s I s a a .9 f .9 m 1/ I 'la 5 3 l2 c D F e H J K L M PATENTEDAUG 2 6 1975 i-ZEET u OF 7 PATENTED AUG 2 6 I975 SHEET 7 OF 7 ZOOM LENSASSEMBLY BACKGROUND OF THE INVENTION One of the more recenttechnological innovations has been the utilization of microfilm to storethe information generated by computers. The computer provides a visualoutput, for example, on a screen of a cathode ray tube, which output isthen photographed onto microfilm. To achieve full utilization ofinformation stored on microfilm, it is desirable to print such variableinformation onto forrns having preprinted information thereon. Thepreprinted forms may comprise business operations letterhead,distinctive logo, or other similar type of non-varying information on acontinuous strip or web. It is necessary, therefore, to transfer orprint the variable prerecorded information from the microfilm onto theweb so that the variable information is accurately registered with thepreprinted information with a minimum of distortion. The availability ofcommercial machines for printing the variable information on microfilmin registration with preprinted information has been extremely limited.

Recently it has been proposed that a xerographic copying machine beemployed to directly utilize microfilm having variable data photographedthereon, the microfilm having the variable data functioning as theoriginal document for copying purposes. A copy medium, preferably a webof paper, would have preprinted, non-variable information providedthereon.

In the type of system described it is desirable to have a system forprojecting the images from the microfilm at various desiredmagnification ratios with a minimum of distortion onto the preprintedweb. In the prior art xerographic systems, copying of microfilm hascustomarily been accomplished by the use of fixed focal length lenses.To change the magnification, it was necessary to change the track length(the overall optical distance from the object to image) and then refocusthe lens system. Alternatively, the prior art provided add lenseswhich'were added to the original lens system to extend the useful rangeof magnification. Magnification would be changed in the former, bymoving the film gate or the image receptor, i.e., xerographic plate ordrum, with their associated mechanisms, or, in the latter situation, byinserting add lens and then refocusing the system. The complexities andinaccuracies with these techniques are quite obvious.

The convenience of a mechanically compensated zoom lens system whichavoids the deficiences noted hereinabove is disclosed, for example, inUS. Pat. Nos. 3,360,325 and 3,640,605 which describe prior art systemsfor solving this problem. Although adequate for the purposes envisionedin the aforementioned patents, the disclosed systems do not meet thenecessary resolution and distortion requirements in the requiredspectral band and magnification ranges as in the projection systemdescribed hereinabove.

SUMMARY OF THE PRESENT INVENTION The present invention provides a zoomlens assembly particularly adapted for projecting images from the objectplane to the image plane at magnifications from approximately 17 timesto approximately 29 times and operating in the wavelength range from0.38 to 0.54 microns.

In particular the zoom lens assembly of the present invention is made upof four members, including a front fixed member, two cam controlledmoving members, and a rear fixed member. A diaphragm is mounted withinthe rear moving member and is controlled by a third cam to maintain aconstant f/number aperture at the long conjugate. The magnification ischanged by rotating the cam sleeve into which two cam slots are cut. Ina preferred embodiment, the cams which control the movable members aredesigned so that equal angular rotations change the magnification byequal amounts.

An object of the present invention is to provide a zoom lens assemblywhich has high resolution and low distortion in a predetermined spectralband and magnification range.

It is still a further object of the present invention to provide a zoomlens assembly made up of four members including a fixed front member,two cam controlled moving members, and a rear fixed member. The cams aredesigned so that equal angular rotations change the magnification byequal amounts. A diaphragm mounted within the rear moving member iscontrolled by a third cam to maintain a constant f/number aperture atthe long conjugate.

It is still a further object of the present invention to provide a novelzoom lens assembly which provides a sharp image and provides a highresolution power at best focus at the image plane.

DESCRIPTION OF THE DRAWINGS For a better understanding of the inventionas well as other objects and further features thereof, reference is madeto the following description which is to be read in conjunction with thefollowing drawings wherein:

FIG. 1 is an optical diagram of one embodiment of the present invention;

FIG. 2 is a chart of a first compilation of constructional data for theembodiment shown in FIG. 1;

FIG. 3 is a chart of a second compilation of constructional data for theembodiment shown in FIG. 1;

FIG. 4 is an optical diagram of a second embodiment of the presentinvention;

FIG. 5 is a chart of a compilation of constructional data for theembodiment shown in FIG. 4;

FIG. 6 is a longitudinal sectional. view of the adjustably mounted lensassembly shown in FIG. 1; and

FIG. 7 is a layout of the cam surfaces utilized to position theadjustable lens elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS front member being identifiedby the reference nu- I meral 20 and being fixed, the second member beingidentified by reference numeral 22 and being movable, I

the third member being designated by reference numeral 24 and beingmovable, and the rear member being identified by reference numeral 26and being fixed.

Member 20 is made up of a double convex lens A which is utilized toadjust the image to focus at the image plane 14. Spaced from positivelens A by an air gap is a negative meniscus element B convex to thefront. Movable member 22 comprises an air spaced triplet comprisingelements C, D, and E. The motion of moving member 22 is computed to holdthe distance from member 20 to the optimum focus adjacent image plane 14at a constant value as the positive zooming member 24 is moved. ElementC is a positive meniscus lens element convex to the front separated fromdouble convex lens element D by an air gap. Element E is a doubleconcave lens element which is cemented to the rear surfaceof lenselement D. Element F, the last element of movable member 22, is a doubleconcave lens element with a weakly curved (almost plane) rear surfaceand is spaced from element E. Elements C, D, E and F essentially form anegative compensating member which compensates for variation in lateralcolor throughout the zooming range. Movable member 24 is the positivezooming member and comprises a negative meniscus element G convex to thefront which is utilized to correct for aberrations such as coma andspherical aberration. Lens element H is spaced from element G by an airgap with a variable iris diaphragm 30 interposed therebetween. ElementH, providing approximately one-half of the positive power of member 24,is a double convex lens element comprising a glass (or other opticalmaterial) with a low dispersion effect.

Spaced from element H is a doublet comprising positive double convexlens element 1 of low negative dispersion and meniscus lens element Jconcave to the front having a high dispersion, lens J being cemented tolens I in a known manner. The doublet substantially corrects forspherical aberration and axial color. In order to improve secondarycolor aberration, a final doublet spaced from doublet l and J andcomprising elements K and L is provided. Positive Element K is ameniscus lens element with a substantially flat front surface which iscemented to negative meniscus lens L concave to the front, each lenscomprising a glass (or other optical material) selected for favorablepartial dispersions in the pertinent spectral range.

The fourth member of the assembly, essentially a field flattener,comprises thick positive meniscus lens M having a substantially flatrear surface.

The front focusing lens A refocuses the image (focused by the movablezoom members 22 and 24 at a plane between the front surface of lens Aand image plane 14) to the object plane 14. The rear focusing member Msimilarly moves the object focus (focused by the zoom members at a planeto the rear of the object plane 12) to the object plane 12.

The two charts set forth in FIGS. 2 and 3 are examples of constructionaldata for two embodiments of the zoom lens assembly shown in FIG. 1. Itshould be noted that radius R of the front surface of element A is shownto be substantially flat and is intended to illustrate both the FIGS. 2and 3 embodiments of R Referring now to FlG. 4, a second embodiment ofthe zoom lens assembly is illustrated. In particular, the zoom lens isdesignated by reference numeral l. the object plane (film plane) of thelens system is designated by the reference numeral 12', and the imageplane of the lens system is designated by the reference numeral 14.

The lens system 10' is made up of four members, in a manner identical tothe system shown in FIG. I, the

front member being identified by the reference numeral 20' and beingfixed, the second member being identified by reference numeral 22' andbeing movable, the third member being designated by reference numeral24' and being movable, and the rear member being identified by referencenumeral 26' and being fixed.

Member 20 is made up of a positive meniscus element A concave to thefront which is utilized to adjust the image to focus at the image plane14'. Spaced from positive lens A by an air gap is a negative meniscuselement B convex to the front. Movable member 22' comprises an airspaced triplet comprising elements C, D, and E. The motion of movingmember 22' is computed to hold the distance from member 20' to theoptimum focus adjacent image plane 14' at a constant value as thepositive zooming member 24 is moved. Element C comprises a positivemeniscus lens element concave to the front and element D comprises adouble convex lens element separated from C by an air gap. Element E isa double concave lens element which is cemented to the rear surface oflens element D. Element F, the last element of movable member 22', is adouble concave lens element, with a weakly curved (almost plane) rearsurface and is spaced from element E. Elements C, D, E and F essentiallyform a negative compensating member which compensates for variation inlateral color throughout the zooming range. Movable member 24 is thepositive zooming member and comprises a negative meniscus element Gconvex to the front which is utilized to correct for aberrations such ascoma and spherical aberration. Lens element H is spaced from element Gby an air gap with a variable iris diaphragm 30' interposedtherebetween. Element H, providing approximately one-half of thepositive power of member 24', is a positive meniscus lens concave to thefront comprising a glass (or other optical material) with a lowdispersion effect. Spaced from element H is a doublet comprising doubleconvex lens element l of low dispersion and negative meniscus lenselement J concave to the front having a high dispersion, lens J beingcemented to lens I in a known manner. The doublet substantially correctsfor spherical aberration and axial color. In order to improve secondarycolor aberration, a final doublet spaced from doublet l and J andcomprising elements K and L is provided. Element K is a double convexlens element which is cemented to negative meniscus lens L concave tothe front, each lens comprising a glass (or other optical material)selected for favorable partial dispensions in the pertinent spectralrange.

The fourth member of the assembly, essentially a field flattener,comprises thick positive meniscus lens element M having a substantiallyflat rear surface.

The front focusing lens A refocuses the image (focused by'the movablezoom members 22' and 24' at a plane between the front surface of lens Aand image plane 14') to the object plane 14'. The rear focusing membersimilarly moves the object focus (focused by the zoom members at a planeto the rear of the object plane 12') to the object plane 12.

The chart set forth in FlG. 5 is the constructional data for the zoomlens assembly shown in FIG. 4.

Referring now to FIG. 6, there is shown a diagrammatic longitudinalsectional view of a lens assembly mount, the lens assembly of FIG. 1being mounted therein (the lens assembly of FIG. 4 may also be similarlymounted). The adjustable mount 40 includes housing 42, and a mountingcollar 44. The mounting collar 44 mounts the housing to an externalapparatus, such as the film projection system described hereinabove.

Lenses A and B of the first fixed member are fixedly mounted withinhousing 42 by retainer member 48 and spacer 50 in a conventional manneras shown. A

The second movable group of lenses C-F are mounted within lens assembly52 in a known manner and separated from the first fixed group by apredetermined distance depending upon the nominal magnification. Thelens elements G-L, comprising the third movable member. are mountedwithin lens assembly 54 and spaced from lens assembly 52 by a similarlypredetermined distance. The fourth member, comprising lens M, is fixedlymounted within housing portion 46. A cam sleeve assembly 60, having agear tooth portion 62 at one end thereof, is so mounted adjacent housing42 such that it overlaps at least a portion of lens assemblies 52 and54. The cam sleeve 60 includes slot portions 64 and 66 into which areinterposed cam followers 68 and 70, respectively. The cam followers,which may comprise a nut, bolt and washer assembly as shown, are fixedlymounted to the respective lens assemblies through the slots 80 and 82.Cam follower 68 is biased by spring member 76 against a finished surfaceof cam slot 64, as shown, and thereby maintains lens assembly 52 at itsnominal axial position. Spring member 78 biases cam follower 70 againstone surface of cam slot 66 and maintains lens assembly 54 in its nominalaxial position. Slots 80 and 82 are provided to allow for axial movement(and to prevent rotation) of lens assemblies 52 and 54. A cover 84 maybe included to prevent dust or other materials from contaminating theoptical elements.

An iris diaphragm 90 is mounted between lenses G and H and moves axiallywith the lens assembly 54. Pin 94 extends through slot 92 and is coupledto diaphragm 90 to control the aperture size. Iris diaphragms of thetype described are commercially available from, for example. llexCorporation, Rochester, NY.

As will be described hereinafter in more detail, the cam slots 64 and 66are so designed that equal angular rotation of cam sleeve 60 willproduce a corresponding equal change in magnification. For systems whichwill utilize the magnification ratio as a control parameter, providing amagnification which is linearly related to the rotation of the camsleeve 60 provides obvious advantages, such as simplicity in the controlmechanism.

To zoom or change magnification of the assembly, a timing belt (notshown) is provided to coact with gear teeth 62. The timing belt, whenenergized, causes cam sleeve 60 to rotate. The cam followers 68 and 70,pro jecting through slots 64 and 66, are forced to traverse the slots ina direction whereby the lens assemblies affixed thereto are driven inthe axial direction from left to right, as viewed from FIG. 6, as thelower pin structure of the cam followers are forced to traverse slots 80and 82.

The movement of lens assembly 54 causes pin 94 to traverse slot 92 in amanner whereby diaphragm 90 is adjusted in a manner such that a constantf/number is maintained at the long conjugate.

The details of the lens mount 40 have not been described since it isbelieved to be within the skill of those involved in the areas ofoptical technology. For example, the patent to Harris et al., US. Pat.No. 3,038,378, describes a typical adjustable lens mount. The presentinvention is, in fact, directed to particular features of the lensmount.

In particular, cam surfaces 64 and 66, shown in a layout form in FIG. 7,have been designed so that equal angular rotation of cam sleeve 60 willcause an equal change in magnification. For example, at the nominal, orinitial setting, magnification is set at 29X. A 40 increment of camsleeve rotation will change the magnification to 26X (decrease of threemagnification levels). The second 40 angular displacement (total of willdecrease the magnification by an equal step to 23X, and so on.

The cam slots may be designed by setting up a computer run on acurve-fitting program with the magnification as the independentvariable.

The data for the lenses shown in FIGS. 1 and 2 for calculating the camslot layout is as follows:

This data was verified to ensure that the best focus remained at thesame film plane, any necessary shifting being accomplished by changingS3 and S6 equally in opposite directions. The nominal magnification wascomputed for a test object of 7 inches diameter at the long conjugate.This was adopted as a standardized specification since it cuts theeffective distortion in half at 29X, where the distortion is a maximum,and maintains the distortion to about 0.1 percent or less at allmagnifications.

The cam shapes were, in the preferred embodiment, computed andfabricated so that equal angular rotations of the cam sleeve wouldproduce equal increments in the magnification. In particular, thefollowing polynomial was set up:

where Si S3, S6 and S11 and where X magnification. The numerical valuesfor the constants A, B, C, D were derived by setting up simultaneouslinear These equations are written out to the required accuracy andsolved by elmination, matrix methods or by fitting quadratic, cubic andsuccessively higher degree equations until the errors of fit becomesufficiently small.

Once the three equations are established, Si is easily computed forsuccessive numerical values of X. For example, for X 29.00, X 28.95, X=28.90. X=

l7.00 would give approximately 241 points on the cams, and if it isdecided to rotate the cams l60, these points would be at every 40. Itwill be noted that $3 and S11 determine the motions of the movingmembers and that S6 is computed to confirm whether the sum of S3, S6 andS11 remains constant.

It should be noted that the procedure described hereinabove may beutilized to calculate cam slot layouts for other optical lensconfigurations in addition to that shown in FIGS. 1 and 2.

The cam slot 92 controlling the iris setting is similarly designed suchthat a particular angular rotation of the cam sleeve 60 will cause pin94 to move along slot 92 such that the iris setting is adjusted toprovide a constant f/number at the long conjugate.

It is convenient to obtain diaphragms which open linearly with respectto the movement of a control lever. The movement is then a function ofS11:

Diaphragm setting K [A-l-B-Sl I+C(Sl l where K is the constant of thediaphragm (or the diaphragm function if not linear), A, B and C arepolynomial coefficients as set forth previously and S11 is the rearvariable space. The diaphragm setting is then computed in degrees andthe cam slot 92 is cut in accordance therewith.

Referring to FIG. 7, the shapes of the cam slots (developed) are showngraphically at 64 and 66. The 29.00X position shown at the top of thegraph is taken as the fiducial position and conveniently as the zeroposition for the cam slot cutting tool. As the cam sleeve is rotated,the cutting tool is moved in accordance with the computed values setforth hereinabove and along the path shown in FIG. 7 to provide thedesired cam slot. For example, for cam slot 66, at 22.27X magnificationthe cam sleeve has rotated 89 44 and S11 has increased from 1.2643 to1.7939 so that the cutting tool must be controlled to be such that ithas moved 0.5296 inches l.7939l .2643) from the fiducial positlon.

The diameter of the iris opening necessary to provide the necessaryf/number at the long conjugate, computed by standard optical techniques,is adjusted as lens assembly 54 is positioned within slot 78. Theangular setting ofiris pin 94 to provide a desired iris opening issupplied by the manufacturer of the iris diaphragm. The length andposition of cam slot 92 is therefore calculated as set forth hereinaboveto provide the necessary angular movement to pin 94, thereby controllingaperture size.

While the invention has been described with reference to its preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the true spirit and scope of theinvention. In addition, many modifications may be made to adapt aparticular situation or material to the teaching of the inventionwithout departing from its essential teachings.

What is claimed is:

I. A zoom lens assembly consisting essentially of an axially fixed frontmember, an axially movable second member, an axially movable thirdmember, and an axially fixed rear fourth member, the first fixed membercomprising, from the front to the rear, a double convex element and anegative meniscus element convex to the front, the axially movablesecond member comprising, from the front to the rear, a positivemeniscus element convex to the front, a doublet comprising a doubleconvex element, the rear surface of which is affixed to a first doubleconcave element, and a second double concave element, said third movablemember comprising, from the front to the rear a negative meniscuselement convex to the front, a first double convex element; a firstdoublet comprising a second double convex element the rear surface ofwhich is affixed to a first negative meniscus element concave to thefront and a second doublet comprising a positive meniscus element, therear surface of which is affixed to a second negative meniscus elementconcave to the front, the fourth fixed member comprising a positivemeniscus element.

2. A zoom lens assembly consisting essentially of an axially fixed frontfirst member, an axially movable second member, an axially movable thirdmember, and an axially fixed rear fourth member, the first fixed membercomprising, from the front to the rear, a positive meniscus elementconcave to the front and a negative meniscus element convex to thefront, the axially movable second member comprising, from the front tothe rear, a positive meniscus element concave to the front, a doubleconvex element, the rear surface of which is affixed to a first doubleconcave element, and a second double concave element, said third movablemember comprising, from the front tothe rear, a negative meniscuselement convex to the front, a positive meniscus element concave to thefront, a first doublet comprising a double convex element, the rearsurface of which is affixed to a negative meniscus element concave tothe front and a second doublet comprising a double convex element, therear surface of which is affixed to a negative meniscus element concaveto the front, and the fourth fixed member comprising a positive meniscuselement.

3. A zoom lens assembly made substantially according to the followingspecifications:

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. I 3,901,585

DATED I August 26, 1975 |NV ENTOR(S) 2 Harold F. Bennett et al It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 9, clalm 4, between llnes 45 and 50,

should read R 2.6149 Between lines 50 and 55,

"R should read R .8475

Column 10, claim 5, between lines 45 and 50, "R

should read R .6968 Between lines 60 and 65,

R 1.4662 soudrea R 1 66 Signed and Scaled this twenty-third D3) OfDecember I 975 [SEAL] Attest:

RUTH C. MASON c. MARSHALL DANN Arresting Officer Commissioner nfParentsand Trademarks

1. A zoom lens assembly consisting essentially of an axially fixed frontmember, an axially movable second member, an axially movable thirdmember, and an axially fixed rear fourth member, the first fixed membercomprising, from the front to the rear, a double convex element and anegative meniscus element convex to the front, the axially movablesecond member comprising, from the front to the rear, a positivemeniscus element convex to the front, a doublet comprising a doubleconvex element, the rear surface of which is affixed to a first doubleconcave element, and a second double concave element, said third movablemember comprising, from the front to the rear a negative meniscuselement convex to the front, a first double convex element; a firstdoublet comprising a second double convex element the rear surface ofwhich is affixed to a first negative meniscus element concave to thefront and a second doublet comprising a positive meniscus element, therear surface of which is affixed to a second negative meniscus elementconcave to the front, the fourth fixed member comprising a positivemeniscus element.
 2. A zoom lens assembly consisting essentially of anaxially fixed front first member, an axially movable second member, anaxially movable third member, and an axially fixed rear fourth member,the first fixed member comprising, from the front to the rear, apositive meniscus element concave to the front and a negative meniscuselement convex to the front, the axially movable second membercomprising, from the front to the rear, a positive meniscus elementconcave to the front, a double convex element, the rear surface of whichis affixed to a first double concave element, and a second doubleconcave element, said third movable member comprising, from the front tothe rear, a negative meniscus element convex to the front, a positivemeniscus element concave to the front, a first doublet comprising adouble convex element, the rear surface of which is affixed to anegative meniscus element concave to the front and a second doubletcomprising a double convex element, the rear surface of which is affixedto a negative meniscus element concave to the front, and the fourthfixed member comprising a positive meniscus element.
 3. A zoom lensassembly made substantially according to the following specifications:4. A zoom lens assembly made substantially according to the followingspecifications:
 5. A zoom lens assembly made substantially according tothe following specifications: